Obesity and smoking are each risk factors for early death, but new research suggests that together they pose a profound mortality risk, HealthDay News reported Nov. 12.

Obese smokers were six to eight times more likely to die during the study period than normal-weight smokers, researchers found. Additionally, smokers with large waists had a five times greater risk of dying than people with the smallest waists who never smoked.

"We found that smoking and obesity are independent predictors of mortality, but smoking and being obese especially increases the mortality risk," said Annemarie Koster, an epidemiologist at the U.S. National Institute on Aging and the lead author of the study.

Data was collected on 3.5 million AARP members who were surveyed on two separate occasions about diet, family history of cancer, physical activity, hormone replacement therapy, weight, waist size, and smoking. The researchers linked the AARP data with death records of the survey participants from 1996 to 2006.

Researchers found that smokers had the highest death rates among all weight levels, but as weight increased so, too, did the death rate.

"If you are overweight and smoke, fixing either one can markedly improve your chances for a normal life span," said David Katz, director of the Prevention Research Center at Yale University School of Medicine.

The study was published in the November 2008 issue of the American Journal of Clinical Nutrition.